Most video playback systems and schemes of today implements some kind of visual search functionality like fast forward function or a skip function arranged to skip between predetermined bookmarks or a predetermined time slot, e.g. 30 seconds of video. This type of functionality is desirable in most video playback systems, but is particularly desirable in surveillance applications where an operator may have to browse through hours of video in order to find a motion video sequence of interest.
In systems where the motion video data is delivered to the motion video playback device from the motion video storage device via a computer network this type of visual search functionality generally is implemented in the client only, i.e. the motion video data for normal playback is streamed or downloaded to the motion video playback device which then is playing back the received motion video data in a playback speed requested by the user. In the case the requested playback speed differs from the playback speed of the streamed motion video, the client changes the playback speed. Alternatively, the motion video storage device stores multiple motion video streams for different playback speeds. However, this later scheme requires an increased amount of storage space in relation to a system storing a motion video stream in one playback speed only.
In U.S. Pat. No. 6,012,091 (the '091 Patent), a video telecommunications server arranged to store video messages and to transmit video messages to a user upon request is described. As described in the '091 Patent, a normal scenario in messaging systems is that the user is playing a video message at normal speed and may wish to return to a previous location in the video at fast reverse in order to replay at normal speed to review some missed action in the video message. In order to enable such rewind functionality, the server stores a sequence of properly decoded frames comprising, for example, every nth decoded frame where n represents the speed-up rate, for example, where n equals 4 or 8, and finally encodes the sequence comprising every nth frame as a fast scan video signal for transmission to the user's video decoder and display. A fast forward bit stream is encoded using only every nth frame, as these frames are independent frames which are not relying on data from other frames in to order represent an image, i.e. fully specified images, and a reverse bit stream is encoded using every nth frame in reverse order.